1. Field of the Invention
The invention relates to a switching system which is adaptable to include a plurality of switches for selectively controlling the application of electrical power to an electrical load.
2. Description of the Prior Art
Numerous clever circuits have been developed in the past for controlling the connection of an electrical supply source to its load. However, generally the wiring of homes and buildings uses conventional switches in line with the circuit from the AC power source to the electrical load. Where light fixtures in a home are to be switched on and off the wiring is of heavy gauge copper or aluminum and runs from the source of the AC power through one or more switches to the electrical load (which would be the light fixture). This results in an expensive wiring installation since the wiring to each switch and each switch itself must be sufficient to carry the total power needed by the electrical load. Such switches need relatively heavy duty contacts and incorporate high voltages which present some risk of shock in the event of failure or improper installation.
It has been known to replace this previously described system with one incorporating relays which can latch either on or off. The individual switches used to control the relays can be operated from a large number of points at low AC voltages with relatively small gauge wire and relatively light duty switch contacts. Normally the control switches do not operate in the conventional toggle fashion to which persons are accustomed but rather have to be operated in one direction to turn the lights on and in another direction to turn the lights off in a momentary contact type of arrangement.
U.S. Pat. No. 3,481,489 to Platzer, Jr. discloses a third type of prior art switching circuit. This circuit incorporates a triac to control the current through a light bulb. The triac is controlled by two separate switches, each of which are single-pole single-throw switches. The switches control AC current which passes through separate windings on a transformer. When the state of either of the switches is changed the state of the conduction of the triac is changed. This provides independent control of the light from two separate locations. This technique, however, is not easily applied to situations which require control at more than two points. Further, transformers of the type disclosed tend to be either expensive or require a relatively large amount of current to achieve reliable control. It may further be noted that in the circuit of Platzer, Jr. U.S. Pat. No. 3,418,489 that high voltage from the source of AC power does appear at the switches.